"One-fifth of adults worldwide will be obese by 2025," The Guardian reports, while The Sun warns that the "UK's population to be fattest in Europe" by the same date. These are just some of the conclusions of a major…

"One-fifth of adults worldwide will be obese by 2025," The Guardian reports, while The Sun warns that the "UK's population to be fattest in Europe" by the same date. These are just some of the conclusions of a major modelling study of global obesity trends.

The study used data covering 19.2 million adults in 186 countries, which was then used to estimate the number of people falling into different body mass index (BMI) categories across the decades, from 1975 to 2014. During that time, the average global BMI for men and women rose by the equivalent of a weight gain of 1.5kg per person, per decade.

High-income English-speaking countries, including the UK, the US, Australia, Ireland and Canada, accounted for some of the biggest rises in BMI. These countries account for more than a quarter of severely obese people in the world.

Interestingly – if worryingly – parts of the world not normally associated with obesity, such as Central and South America, the Middle East and China, are also expected to develop high rates of obesity in the future.

In sharp contrast, the spectre of malnutrition doesn't seem to be going anywhere. Parts of Africa and south Asia still have high rates of people who are underweight: about a quarter of women living in south Asia are underweight. This trend is not expected to change.

The scientists who compiled the data warned that the chances of meeting the global target to halt the rise in obesity were "virtually zero".

The 'fat men (and women) of Europe'

According to data from The Lancet, the three fattest nations in Europe by 2025 are expected to be:

women:

the UK – 38% of women are expected to be obese

Ireland – 37%

Malta – 34%

men:

the UK – 38%

Ireland – 38%

Lithuania – 36%

Still, this is not as bad as our American cousins, where 43% of women and 45% men are expected to be obese.

Where did the story come from?

The study was carried out by researchers from many different institutions, led by Imperial College London, and was funded by The Wellcome Trust and Grand Challenges Canada.

The UK media mainly focused on information not found in the published study but included in a press release sent out by The Lancet.

This information gave estimations of what the UK's obesity rates might be in 2025, compared with other European countries, presumably based on trends in the data. However, we don't know how these calculations were made, so we can't tell how accurate they are.

Only BBC News and The Independent picked up on the sobering fact that we may end up in a world where a majority of the population are obese, while others continue to go hungry.

An honourable mention has to go to The Sun's headline writers, who gave us "Lard of Hope 'n Glory – UK's population to be fattest in Europe by 2025".

What kind of research was this?

This was an analysis of measurement studies done in countries around the world between 1975 and 2014.

The data from the studies was pooled to give a global picture of how the weight profile of the global population has changed.

What did the research involve?

The researchers looked for population-based studies that measured people's height, weight, gender and age, then combined them to give the best estimate of BMI ranges for 200 countries and 21 regions in each year.

They used estimates to fill in data for countries where there had been no or insufficient studies. They looked at the way BMI categories had changed over time for different countries, and calculated the chances of each country meeting the global target to halt the rise in obesity.

The analysis included 1,698 studies from 186 countries, covering more than 19 million people. Researchers restricted the studies to those where people had been measured by a researcher, rather than reporting on their own height and weight.

The researchers then used statistical techniques to test the validity of the estimates they made.

What were the basic results?

Average body mass index rose globally from 1975 to 2014 for men and women. However, it's more interesting to look at the data for individual regions or countries, as there is so much variation between regions.

In the UK, the average BMI for men rose from 24.1 in 1975 to 27.4 in 2014. For women, BMI went from 23.4 to 27. A BMI of 18.5 to 24.9 is considered ideal for an adult.

The rise for both sexes was about 1kg/m2 each decade, although that slowed to about 0.5kg/m2 from 2005-14. The UK has 6.8 million obese men – the eighth highest country in the world – and 7.7 million obese women – the eleventh highest country in the world.

China and the US now have the most obese people in the world, with the US having the most severely obese people of any country. China also comes second in the number of underweight men and women, after India.

The researchers say the trend of increasing obesity slowed among some countries after 2000, notably in countries with high incomes, perhaps as a result of increased concern about obesity.

How did the researchers interpret the results?

The researchers concluded that no country has more than a 50% chance of halting the growth of obesity on current trends, and the UK's chances are between 0% and 25%. They said: "Some high-income and middle-income regions are now facing an epidemic of severe obesity."

They went on to say rising obesity levels have not yet shown an increase in earlier deaths, but this may be because of the availability of drugs to combat high blood pressure, high cholesterol and diabetes in richer countries.

The researchers said even these drugs "will not be able to fully address the hazards of such high BMI levels" in the future, warning that "bariatric surgery [weight loss surgery] might be the most effective intervention".

Conclusion

The figures in the study make for startling reading. Although it's difficult to draw conclusions from a mass of data covering the whole world, it seems clear that adults are becoming progressively heavier, and high-income countries such as the US and UK now have a large proportion of adults who weigh more than is healthy.

The study relies on hundreds of different studies carried out by different organisations, so it is subject to any inaccuracies that might have happened during the measurement and recording process.

However, the researchers only chose studies that had independent measurements of weight and height, so the overall results should be more accurate than if they'd relied on self-reported measurements.

It is now recognised that obesity can often start in childhood. The researchers noted that trends in childhood obesity were not studied here because of difficulties in standardising the measures.

Despite the lack of success in halting the rise in adults, preventative public health interventions for children and families may hold out more promise.

What is less clear is the impact of this global weight gain. As an accompanying editorial points out, global life expectancy has been rising at the same time as BMI, by over 10 years during the study period.

So are we getting "healthier but fatter", as the editorial suggests? We know obesity increases the chances of many life-threatening diseases, including diabetes, heart disease and some cancers. It may be, as the study authors suggest, that modern medicine has managed to keep up with rising obesity so far.

We shouldn't ignore the number of people who are still underweight in the world. While this is a small proportion of people in rich countries like the UK, more than 200 million people in India are underweight for their height.

China and India together account for more than half of the men and women who are underweight in the world. It is striking that China and India both also feature in the top 10 countries with obesity in men.

The release of the data has been accompanied by calls from health campaigners for the government to do more to tackle unhealthy eating and obesity.